The present invention relates to a hard disc measuring apparatus. More specifically, the invention relates to measuring a reference value Track Average Amplitude (TAA), which is an average level amplitude value of a track, while at the same time accurately detecting defects in the hard disc tracks.
In the conventional hard disc measuring apparatus, read/write means writes signals on the hard disc after an average track level value is read out by the read/write means. This average track level value is used as a reference value TAA. A read value which takes on a certain level below the reference value TAA is known as an MP (Missing-Pulse) value. A read value which takes on a certain level above the reference value TAA is known as an EP (Extra-Pulse) value after attempted erasure of the signal.
Any portion of the track at which it is impossible to write to sufficiently even after the read/write means attempts to write the signal to the hard disc, or at which a written signal is not completely erased even though it should have been erased, is considered to have a defect.
There are two methods for determining the reference value TAA using the conventional hard disc measuring apparatus and for detecting a defect in the tracks of the hard disc, as described in FIGS. 5(a) and 5(b). The first method is based on the TAA of a finished track. This is structured to measure the processing track (the track presently under a measuring process) based on the TAA of a finished track (a prior or previous track already measured one track earlier).
The second method is based on the TAA of the processing track. This is structured to measure a processing track based on the TAA of the processing track itself after measurement of the TAA of the processing track.
The conventional measuring apparatus has problems associated with it. In the first method described above, the TAA of a track prior to the track being measured is used alternatively for the reference value TAA of the processing track to improve throughput, in which the reference value TAA can be measured, while at the same time a defect can be detected.
However, in this method, the reference value TAA is different from the TAA of the track being processed for a defect. The reference value TAA includes dispersion in the writing and reading of signals, which produces dispersion in the process of detecting a defect of the track in the hard disc.
In the second method described above, the written signals for measuring the reference value TAA and for detecting a defect become the same, provided that the value of the TAA of a track being measured is used as the reference value TAA. The reference value TAA includes dispersion merely in the reading of signals, and defect detecting signals having less dispersion are advantageous over the first method.
However, this method has a problem relating to deteriorating throughput because the reference value TAA has to be read before detecting a defect.